The present invention relates to a mechanism for threading an electrode wire through a starter hole or aperture in a workpiece prior to cutting the workpiece by electrical discharges.
Prior to starting a cut in a workpiece by way of the electrode wire of a travelling wire EDM apparatus, a starter hole or aperture is made in the workpiece, the electrode wire is threaded through the starter hole or aperture, and subsequently the wire is tensioned and displaced longitudinally through the machining zone between the wire and the workpiece. In the prior art electrode wire threading devices, the contact supplying electrical current to the wire and the wire guiding surface must be retracted to free the wire path until the end of the wire is taken up by the wire conveying mechanism, and they must be extended to their normal operating positions after engagement of the end of the wire in the conveying mechanism. Those functions can be achieved only by relatively complex mechanisms.